We hypothesize that dyspnea and disability in chronic obstructive lung disease (COLD) is due to inspiratory muscle dysfunction. If so, many patients with severe COLD may have chronic inspiratory muscle fatigue which can be treated by ventilatory muscle rest (VMR). Thus, a randomized controlled clinical trial has been mounted to assess whether VMR will 1) improve exercise perfor- mance; 2) alleviate the sensation of dyspnea; and 3) improve measurable quality of life for patients with severe irreversible chronic obstructive lung disease (COLD). Patients are randomized to one of two groups: active or sham VMR. Throughout enrollment, records are being kept of all patients examined. Reasons for exclusions are noted to allow identification of potential distortions in the study population and to guide appropriate extrapolation. The primary outcome of interest is the change in exercise tolerance as measured by the endurance time at 2/3 of peak power output. Secondary outcomes, including the distance walked in 6 minutes, level of dyspnea, arterial blood gases, and measurable quality of life, are expected to reflect similar patterns of change. Preliminary data, from uncontrolled trials, have shown substantial improvement resulting from VMR. We hope to assess the effectiveness of this intervention in a more rigorously controlled investigation before its diffusion renders such controlled study more difficult. If successful, this new form of low-cost therapy may revolutionize the rehabilitation of patients with severe COLD.